Till the year 1079 the Persian year resembled that of the ancient Egyptians, consisting of 365 days without intercalation; but at that time the Persian calendar was reformed by Jelal ud-Din Malik Shah, sultan of Khorasan, and a method of intercalation adopted which, though less convenient, is considerably more accurate than the Julian.
For The Sake Of Greater Generality, The Days Of The Week Are Denoted By The First Seven Letters Of The Alphabet, A, B, C, D, E, F, G, Which Are Placed In The Calendar Beside The Days Of The Year, So That A Stands Opposite The First Day Of January, B Opposite The Second, And So On To G, Which Stands Opposite The Seventh; After Which A Returns To The Eighth, And So On Through The 365 Days Of The Year.
The Solar Astronomical Year Is The Period Of Time In Which The Earth Performs A Revolution In Its Orbit About The Sun, Or Passes From Any Point Of The Ecliptic To The Same Point Again; And Consists Of 365 Days 5 Hours 48 Min.
These are easily calculated on the assumption first that the observations were correctly made, secondly that the calendrical dates are in the year of 365 days beginning on.
Now, As The Year Consists Of 365 Days And A Fraction, And 365 Is A Number Not Divisible By 12, It Is Impossible That The Months Can All Be Of The Same Length And At The Same Time Include All The Days Of The Year.